precise positioning gnss applications · machine guidance precision agriculture • surveying &...

31.5.2012

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Precise Point Positioning:Is the Era of Differential GNSS Positioning Drawing to an End?

School of Surveying & Spatial Information Systems, UNSW, Sydney, Australia

Chris Rizos1, Volker Janssen2, Craig Roberts1, Thomas Grinter2

1 School of Surveying & Spatial Information Systems, UNSW, Australia

2 Land & Property Information, Dept. of Finance & Services, NSW, Australia

Building Construction

Land Surveying

Port Operations

Geodesy

Machine Guidance Precision Agriculture

• Surveying & mapping

• Precise kinematic apps, such as machine guidance/control

• Define/monitor datum, geodesy apps, etc.

• Precise georeferencing of airborne or terrestrial scanning/imaging sensors

Monitoring Rapid Mobile Mapping

Precise Positioning GNSS Applications

31.5.2012

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FIG Working Week, Rome, Italy, 6-10 May 2012

Scientific geodesy

How “precise”?

1cm 2cm Sub-dm 1dm

Datum

Surveying

Engineering & construction

Precision agriculture

Advanced ITS

Mapping

Sensor georeferencing

Machine automation

Deformation surveys

Offshore engineering

LEO POD

Disaster response


For almost all Precise Positioning GNSS applications the differentialGNSS technique has been the onlymeans of satisfying accuracy requirements...

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Over many years a wide range of DGNSS techniques have evolved... balancing constraints of accuracy, complexity, timeliness, cost & performance... specialised HW, SW & operations

Global CORS to support geodetic apps...

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CORS Infrastructure…commercial

10,000s of CORS...Massive investment?


Precise Point Positioning (PPP) has evolved and some claim it will address weakness of DGNSS, the need for reference receiver infrastructure...

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Will PPP displace DGNSS?... Are they complementary? Do they address different markets? Can they be used interchangeably?


GNSS Satellite Orbit and Clock Corrections

GNSS User

IGS CORS Network

GNSS Constellation

How It Works

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Correction Type PPP Differential GNSS

Satellite Specific errors

Precise satellite clock corrections

Satellite antenna phase centre offset

Satellite antenna phase centre variation

Precise satellite orbits /

Group delay differential (L1 only)

Relativity

Satellite antenna phase wind-up error

Receiver Specific Errors

Receiver antenna phase centre offset

Receiver antenna phase centre variations

Receiver antenna phase wind-up

Geophysical Models

Solid earth tide displacements

Ocean loading

Polar tides

Plate tectonic motion

Atmospheric Modelling

Troposphere

Ionosphere (L1 only)

Comparing PPP & DGNSS...


International GNSS Service•Provides Precise Satellite Orbits &

Clock Corrections

How It Works

Real-time IGS Orbit

Clock

<10 cm

0.15 ns

10-20 secs

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X Y Z

IGS CORS Network

GNSS User

GNSS Satellite Orbit and Clock Corrections

GNSS Constellation

PPP processor

Geophysical/Atmospheric, Receiver/Satellite Specific Modelling

Post-Processed (“Standard”) PPP


Comparing “apples” & “oranges”... By removing CORS/data requirement, users have lower accuracy (kinematic), non-RT positioning on non-local datum...

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T. Horvath, “PPP-RTK: Friend or Foe?”, BKG PPP-RTK & Open Standards Symposium, Frankfurt, Germany, 12-13 March 2012


PPP has other challenges... to reach RTK performance need:industry message format stds, higher accuracy orbit/clk products, convenient transmission, commercial Rx (non-proprietary) implementations, AND some local CORS

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• Real-time product generation is part of IGS Strategic Plan, started 2002

• Infrastructure:

– More than 120 active real-time stations

– Data streaming using NTRIP

– Close link to RTCM...joint WG established

• Analysis:

– 8 real-time Analysis Centres (one in China)

– Real-time orbit & sat clock combination...can support RT-PPP

• Future:

– Real-time service to be launched mid-2012...GPS-only

– Satellite clock corrections, orbits, ionosphere corrections

– Include new systems and signals

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IGS Real-Time Pilot Project


Slow convergence...

30 cm after 10 min20 cm after 20 min10 cm after 50 min

http://igs.bkg.bund.de/ntrip/ppp

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RT-IGS... supporting RT-PPP

http://igs.bkg.bund.de/ntrip/ppp


Can speed up convergence...... Rapid OTF ambiguity resolution...with local CORS-generated atmospheric correction messages... Or start from “known point”...

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IGS CORS Network

GNSS User

GNSS Satellite Orbits

GNSS Constellation

Regional CORS Network

X Y Z

PPP Network Process (Satellite Clock Estimates + Additional Biases)

Real-Time PPP (“PPP-RTK”)


• Real-time corrections... from IGS or commercial entities?

• Orbit reference point... CoM or APC?

• Implementation of industry standards... RTCM HP-MSM, RTCM SSR

• Real-time “latency”... 10-20 seconds

• RT-IGS is GPS-only... GPS + Glonass in 2013?

• Transmission of RTCM SSR... Satcoms or terrestrial?

• Cm-level accuracy for “RTK-PPP”... Local datum (like DGNSS)?

• Cooperation of CORS operators, RTK-PPP message providers, RT-IGS, comms operators, Rx manufacturers...

Real-Time PPP... some issues

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All the disadvantages of PPP & increased complexity & still some CORS requirements...!!!!Less CORS? 100-200km spacing? Yes less than RTK/NRTK, but what about future triple-freq DGNSS?


Accuracy “creep” from dm->sub-dm->cm...... How is the orbit/clk information now at sub-cm level (remember PDOP effect)? With “no” latency?”... Implying higher performance than RT-IGS...Is PPP-RTK being over-sold?

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PPP vs DGNSS...

• Another tool for the GNSS user... But performance of RTK-DGNSS relies on CORS infrastructure design.

• Should we be phasing out CORS investment because “PPP-RTK” is improving?...NO.

• Still need sparse CORS for “PPP-RTK”... So care must be taken to not abandon CORS networks.

• PPP techniques fail on “transparency” grounds...

precise positioning gnss applications · machine guidance precision agriculture • surveying &...

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